The past two decades have seen the introduction of particulate filters and catalytic converters as cleansing means for exhaust gases, and the rapid growth of such use.
A catalytic converter is a porous, or multichannel, refractory body having a catalytic material, e.g., platinum particles, deposited on the walls of the body. The body may also be referred to as a honeycomb body. Exhaust gases are passed through the body to catalytically convert the gases to a non-toxic form. For example, carbon monoxide (CO) may be oxidized to carbon dioxide (CO.sub.2). The particulate filter also utilizes a porous, or multichannel, refractory body, but does not require a catalyst.
It is common practice to mount the refractory body in a metal container known as a can. The can may then be inserted in a vehicular exhaust line by welding end portions of the can into the line.
When thus installed in a vehicle, the refractory body may be subject to considerable vibration. Since the body must have very thin walls, it tends to be rather fragile, particularly when formed from fired ceramic material.
Accordingly, it has become common practice to provide a barrier layer between the can and the refractory body. For this purpose, a can somewhat larger than the body is employed to leave an intermediate space between the body and the can. The body is then wrapped in a refractory fabric, or other packing, to fill the space and act as a cushion.
This practice entails a separate operation, which is time consuming and adds to the cost. The need for a more efficient practice has been evident. Nevertheless, the wrapping procedure has continued in use for lack of an effective alternative.